3V, Ultra-Low-Power

Quadrature Modulator

6

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Applications Information

The MAX2452 quadrature modulator is designed to

upconvert I and Q baseband signals to IF frequencies

up to 80MHz. Figure 2 shows a typical application

block diagram, in which the MAX2452 is used for the

first upconversion in a dual-conversion transmitter.

Figure 3 shows an implementation of a resonant tank

circuit. The inductor, two capacitors, and a dual varac-

tor form the resonant circuit of the oscillator. The fre-

quency range of the oscillator shown in Figure 3 is

130MHz to 160MHz. The inductor is directly connected

across the local oscillator’s tank ports so that it will not

lock up the oscillator in a stable state during start-up.

The two 33pF capacitors increase the Q of the resonant

circuit and reduce the VCO gain. They can be changed

to meet individual applications requirements. The oscil-

lation frequency can be determined using the following

formula:

tance.

To alter the oscillation frequency range, change the

inductance, the capacitance, or both. Make sure the Q

of the resonant tank does not drop below 35.

Ω (see Figure 1).

The oscillation frequency can be changed by altering

MAX2452

DSP

PROCESSING

0°

I

Q

÷8

90°

UP CONVERTER

Σ

Figure 2. Typical Application Block Diagram

C1 = 33pF

10k

0.1

µF

1/2KV1410

1/2KV1410

L = 100nH

47k

47k

C2 = 33pF

TANK

TANK

Figure 3. Typical Resonant Tank Circuit

f

LC

where

C

CC

C

C

and

LL

L

o

EQ

EQ

EQ

VAR

STRAY

EQ

STRAY

=

=

++

+

=+

1

2

1

1

1

1

2

2

π

QR

C

L

EQ

EQ

EQ

=